As shown in FIG. 21, a conventional pipeline closing apparatus includes a bottomed tubular lid member 7 attachable to a downstream end portion of a sluice valve for closing an end opening of a branch pipe diverging from and connected to a fluid transmitting main and having the sluice valve disposed in an intermediate portion thereof, a cylindrical first control shaft 8 extending through the lid member 7 to be axially slidable in sealed condition, and a second control shaft 9 extending through the first control shaft 8 to be axially slidable. The first control shaft 8 and second control shaft 9 have pressing plates 10 and 11 attached to inward end regions thereof, respectively. An elastic annular member 12 having a circular cross section is disposed between the pressing plates 10 and 11 to be elastically deformable, by being clamped and pressed by the pair of pressing plates 10 and 11 from axial directions, to a diameter-increased position in tight contact with an inner peripheral surface of the branch pipe to block between the inner peripheral surface and outer peripheral portions of the two pressing plates 10 and 11. Further, a retaining device D is provided as having engaging link pairs 13 and 14 arranged in three circumferential positions and extending between the inward end of the second control shaft 9 and the first pressing plate 10 disposed upstream, for flexing and bulging to a diameter-increased position to engage a large diameter pipe portion formed upstream of a blocked position by the elastic annular member 12, in response to an outward sliding movement of the second control shaft 9 relative to the first control shaft 8.
The retaining device D includes a mounting tubular member 21 slidably fitted on the inward end portion of the second control shaft 9 and having second connecting elements 22 provided in three circumferential positions on an outer peripheral surface thereof to which to ends of the upstream engaging links 13 pivotably connected. Ends of the downstream engaging links 14 are pivotably connected to first connecting elements 20 provided in three circumferential positions on an end surface of the upstream second pressing plate 11. Further, a stopper nut 15 and a lock nut 16 are screwed to the inward end portion of the second control shaft 9 for determining a maximum upstream movement position of the second pressing plate 11 relative to the second control shaft 9 (see Patent Documents 1 and 2, for example).
Patent Document 1: Utility Model Publication No. 4-3196
Patent Document 2: Patent Publication No. 7-81669